1. Field of the Invention
The present invention relates to round-bottom pyrometallergical furnaces for the smelting, converting, or melting of concentrates, mattes, or metals; and more particularly to the construction of tap holes in the brick hearth and lower walls in a furnace refractory where tap hole brick linings can slide inside a conduit, shell, sleeve, water-cooled block or similar structure to accommodate growth in the hearth brick.
2. Description of the Prior Art
One type of smelting furnace for winning copper from ore is built with vertical, cylindrical, steel containment shells with layers of refractory bricks inside the walls and a downwardly dished bottom. A hearth brick sub-layer on the bottom is covered with a brick hearth working layer. The refractory brick layers inside the steel containment shells can withstand the very high operating temperatures usual to the smelting of copper concentrate, and the outer shell provides the necessary containment and support.
Hearth bricks swell up in size over their operational lives as the bricks slowly absorb molecules of metal. Many expensive and complex ways have been devised over the years to keep the refractory bricks tightly pressed together as they swell so that liquid metal, matte, or slag cannot leak through the gaps. For example, so-called “flexible shells” bind adjoining overlapping or segmented plates together using a combination of springs, tie rods, or levers and rods. The loose plate construction can allow for quite a lot of expansion and contraction. However, the cost of these kinds of containment shells is prohibitive.
Rigid hearth containment shells are much less expensive since they are constructed as a single rigid piece that does not require plate binding mechanisms. But conventional ways of keeping the hearth bricks together under the right pressures for these rigid shells accommodates only very limited growth in the hearth brick before shutdown and replacement with new brick is required.
Conventional systems are normally designed to accommodate the thermal expansion of the bricks, but do not maintain the pressure when the bricks cool down and shrink. This allows gaps to form which can invite molten materials to penetrate the brick joints. When the furnace finally reheats, the hearth is incrementally increased in diameter by the new material frozen in the joints. It therefore follows that extending the service life of the hearth bricks translates directly into substantial savings in the maintenance costs because shutdowns are fewer and less frequent, and not as many brick replacements are needed over the life of the furnace.
A basic problem with the design of circular furnaces has been the hearths tend to expand more than do the walls. This is especially pronounced if the walls are water cooled. What is needed are designs that can accommodate both hearth expansion and lesser expansions in the lower wall brick and any refractory.